@kite722 custom skins and the ability to carry 45,659,776 kilograms of blocks.
As measured by 1 cubic meter of gold x64 in a stack times the 37 total player slots.
Downside... you can only ever "free jump" 1 meter.
If it's like Minecraft, what about the other dimensions? The End may be difficult to go to, as creating End portals is impossible in survival, but the Nether would work. And potions, things can get interesting if he could mass produce potions.
This is based on a novel. Unfortunately there is no translated version of the Light novel or the Web novel (or at least I haven't been able to find it), you can find the Web novel version here: https://ncode.syosetu.com/n3742ey/.
If you use the Chrome browser you can use the automatic translation tool, the translation level is quite good, with 80% to 85% comprehension. I hope you enjoy it.